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Heat transfer in nuclear fuel assemblies is limited by onset of the boiling crisis, called CHF. CHF is indicated by a sudden rise of surface temperature (for example, of the fuel rod cladding) due to the decrease in heat transfer from the surface to the fluid. CHF can not be predicted by pure analytical modeling. Exact knowledge of CHF initiation for all thermal-hydraulic initial conditions is a mandatory prerequisite for licensing of nuclear fuel assembly designs. Fuel assembly design-specific CHF correlations have to be developed and validated.

Therefore, CHF tests are performed under realistic boiling water reactor (BWR) or pressurized water reactor (PWR) conditions to generate a CHF database.

The Karlstein Thermal Hydraulic Test Loop (KATHY) is designed for the performance of CHF tests under full-scale conditions to determine the onset of CHF inside electrically heated fuel assemblies which are geometrically identical to real fuel assemblies.
This is a challenging task: high electrical power and current levels have to be precisely handled and quickly controlled when sudden CHF occurs. Determining the onset of CHF requires sophisticated and robust instrumentation operating at high pressures and temperatures.

Your Benefits

  • Full-scale test conditions reduce the need for subsequent modeling
  • Precise test performance at high but fine tunable power levels: maximum 20 MW
  • Wide range of testable fuel designs due to more than 2,500 heater rods in stock
  • Benchmarked against OMEGA Loop (CEA), ATLAS Loop (GE) and HTRF Loop (CU)
  • Accredited test and inspection body and accepted by ILAC
  • Open to external customers

Interested in KATHY Loop for Critical Heat Flux Tests?

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Thermo-Hydraulic Platform qualified as test and inspection body